1. Field of the Invention
The present invention relates to a method of making a semiconductor device of the type which comprises a semiconductor chip bonded to a substrate by flip-chip bonding with an adhesive sealing interposed between the semiconductor chip and the substrate. The present invention also relates to a semiconductor device made by such a method.
2. Description of the Related Art
In a semiconductor device for use in a high-end apparatus such as a super computer, an LSI chip is bonded to an MCM (Multi-Chip Module) substrate by flip-chip bonding using solder bumps for realizing a high performance and high-density mounting. Generally, in the flip-chip bonding, a gap between the LSI chip and the MCM substrate is sealed with a resin for preventing air or dust from entering the gap.
Recently, the flip-chip bonding is increasingly utilized also for making a semiconductor device for use in a middle-end or low-end apparatus. In such a semiconductor device, a substrate such as a buildup substrate or a glass ceramic substrate is often used for mounting an LSI chip to realize a cost reduction. However, a substrate of these kinds differs largely from an LSI chip in coefficient of thermal expansion, which may lead to the generation of large thermal stresses and thereby result in unexpected detachment of solder bumps from the electrodes of the substrate and/or the electrodes of the chip. Therefore, in a semiconductor device for use in a middle-end or low-end apparatus, the adhesive sealing at the bond gap is required to enhance the bonding reliability between the chip and the substrate in addition to preventing the entry of air and/or dust.
For example, JP-A-11-106480 and JP-A-11-106481 propose the use of a sealing adhesive having a relatively high adhesion for enhancing the bonding reliability between the substrate and the chip.
To provide a semiconductor device, an LSI chip is mounted to a substrate by flip-chip bonding, and the bonded portion is sealed with a resin. The assembly of the LSI chip and the substrate is then mounted to a mother board with the substrate oriented toward the mother board, thereby providing a semiconductor device. In mounting the chip-substrate assembly to the mother board, use may be made of BGA (Ball Grid Array), CSP (Chip Scale Package) or PGA (Pin Grid Array) for mounting the substrate to the mother board via arrays of solder bumps or arrays of solder pins. In any of these, the chip-substrate assembly and the mother board are bonded by reflowing the solder bumps or pins. Thus, the chip-substrate assembly is subjected to heating at a high temperature. As a result, the adhesive sealing may suffer cracks and/or release from the substrate and/or the chip due to the deformation of the LSI chip and the substrate or due to thermal stresss generated in the adhesive sealing. This may lead to removal of the solder bumps or pins, which may, in turn, cause damage to the chip electrodes. Such a damage is remarkable at the electrodes provided at a peripheral portion of the LSI chip, because the LSI chip warps largely at the peripheral portion. Moreover, the bumps for bonding the chip to the substrate may be re-melted by the reflow heating and flow into the cracks formed in the adhesive sealing or the removed portion of the adhesive sealing. This may cause adjacent bumps to be electrically connected to each other to result in shorting of the bumps. In this way, the prior art methods for making a semiconductor device are still insufficient in terms of the bonding reliability between the LSI chip and the substrate.